Generally, the above type of operating lever, as disclosed in Japanese Utility Model Laid-Open Gazette No. Sho 58-98,291, is provided with a boss having a winding portion for a control wire, an operating portion connected to one side of the winding portion, and a retaining portion retaining one end of the wire. The boss is supported at its central portion rotatably to a lever shaft of a fixing member fixed to the bicycle frame. The control wire is guided into a winding groove recessed in the outer periphery of the boss and drawn out therefrom to be connected at its other end to a front or rear derailleur. The operating portion is operated in swinging motion so as to wind up the wire onto the winding portion.
Also, the above speed-change operating lever is provided with a positioning mechanism comprising a positioning member having a plurality of engaging portions and an engaging member engageable with one of the engaging portions, such that the positioning mechanism maintains the speed-change operating position get by the lever or with a friction portion which has applied thereto a frictional resistance against rotation so as to maintain thereby the set speed-change position.
The conventional speed-change operating lever, however, has a constant winding amount of the control wire with respect to an operating stroke of the lever, thereby creating the following problem:
Where the operating lever is provided with a positioning mechanism and the winding portion at the lever has a constant outer diameter to thereby fix the wire winding amount, the engaging portions for setting the speed change stages are spaced from each other at a predetermined interval, whereby a stroke of the wire with respect to the operating stroke of the lever for each engaging portion is determined.
However, different multistage sprocket assemblies exist, so that, when the number of sprockets is changed from six to seven, in other words, when the number of sprockets exceeds a predetermined value, an axial interval between each sprocket becomes smaller.
Therefore, where the intervals between the respective sprockets change because the number of sprockets changes or for other reasons, the lever using the aforesaid positioning mechanism cannot be used with the speed change operating device. This is because, when such lever is applied to a multistage sprocket assembly having smaller intervals between the respective sprockets, an amount of movement of the derailleur operated by the operating lever stroke preset by the positioning device does not correspond to the different interval between the respective sprockets.
Where the operating lever is provided with a friction portion as described above, the operator can operate the lever to desirably decide the lever stroke, so that the above problem does not arise. However, when the speed-change operating lever is operated, there is an operation range easy to use by him, but when the interval between the respective sprockets changes, the operation range shifts, thereby creating a problem in that the speed change efficiency deteriorates.
Although the operation range is variable for the operator, the conventional lever has a preset range and the position of the operating portion with respect to the bicycle frame, whereby an optimum operation range for the operator and the speed change position with respect to the bicycle frame cannot be selected.